Introduction and Summary

Cysts and trophozoites must be examined
carefully in different fields of view and measurement is often essential.
Objects such as epithelial cells and macrophages are around the same size as
amoebic trophozoites: the latter may also move and contain red blood cells.

Plant hairs and fibers are easily confused with larvae; algae such as
Psorospermium haeckelii may be found in the feces of patients who have eaten
crayfish.

Earthworms may resemble roundworms.

A variety of non-pathogenic ova,
cysts and parasites resemble pathogens in terms of size and morphology and
careful examination is essential. Eggs of Heterodera, a parasitic
nematode of root vegetables, may resemble hookworm eggs. Eggs originating from
harmless mites in cereals or flour could be confused with hookworm ova but are
usually larger. We recently encountered 160 micron "Schistosome ova" in the
urine of a patient complaining of hematuria: we suspected Schistosoma
haematobium but, on closer analysis, the eggs contained unidentified
insects. This volume provides examples of artifacts that may be confused for
parasitic life stages. Artifacts should be considered on the basis of size,
shape, lack of organelles and defining feature, and variable reactivity with
common stains.

Red and White Blood Cells

Red blood cells and a variety of white blood
cells can be easily mistaken for parasitic cells or cysts when observed with
microscopy.

Charcot-Leyden crystals are a product of
eosinophil breakdown and are, therefore, occasionally found in feces of patients
suffering from parasitic disease. They appear red when stained with in a
trichrome fecal preparation.

Image
13-5.
Image illustratingRed Blood Cells in slide preparation. RBC’s may
appear to have a central body and a rim of cytoplasm or granules which could be
mistaken for Blastocystis hominis. (SOURCE: Unknown)

Fat
Globules

Fat globules present in a fecal slide preparation may appear similar to
parasitic cysts or cell bodies.

Emulsifying agents are a useful tool to
eliminate potential confusion involving fat globules. The removal of such
particles from slide preparations will undoubtedly reduce cases of misdiagnosis.

Yeast Cells

Yeast may resemble protozoan cysts because they
are uniform in color, have few inclusions and no nucleus. Yeast could also be
confused with small protozoans like E. nana or with Cryptosporidium
or Cyclospora oocysts in wet preparation. In acid-fast stains, the
oocysts of Cryptosporidium and Cyclospora species stain pink to
red. Yeasts are not acid fast and stain green.

Image 13-17. Image
illustrating pollen cells in slide preparation. Similar to Taenia eggs,
but distinguished by uneven thickness of the wall and lack of internal contents
do not suggest an egg. (SOURCE: Unknown)

Hair

Animal and plant hairs are most often and easily
mistaken for parasitic nematode worms. Their size and shape may be comparable in
many cases, but a lack of internal definition will identify the artifact when
compared to the worm. Although nematodes are non-segmented and externally simple
organisms, they will often show unique structural characteristics under close
examination.

Insect
Eggs

Plant
Parasites

Image 13-21.
Image illustrating Heterodera spp. in slide preparation. Such parasitic
nematodes attack root vegetables such as beetroot, turnips and radishes. Their
eggs are 80-120mm
by 25-40 mm
and can conceivably be confused with hookworm eggs. (SOURCE: Unknown)

Earthworms

Image
13-22. Image
illustrating an Annelid earthworm in detritus. They belong to the Annelida (Lumbricus
and Allolobophora) and are elongated, segmented and circular in section and are
occasionally confused with Ascaris. They have a purple-brown dorsal
surface and a paler ventral surface, swell out at around segment 12 and possess
a marked thickening (the clitellum) a third of the way from the anterior.
(SOURCE: Unknown)